Beyond basic pageRank principles
Quantity of Links
If a further 25 documents reference the original paper, it gains 25 additional "votes".
The same principle applied to web sites is based on the idea that a link from one site to another is the equivalent of a reference, and thus a "vote".
So if a web site has 26 links in to it ("inbound links") from other sites, it has 26 "votes".
Quality of Links
If Site A is seen as being an "authority" on the subject of "small business" (see the section Credibility and Authority), a link to Site B from Site A will count as a higher-value "vote" for the subject of "small business", than if Site A was not seen as being an "authority".
Certain sites, such as www.bbc.co.uk, are considered to be "authorities" on virtually everything. Thus a link from any page on such a site will be more valuable as a "vote" than many links from "less-authoritative" sites.